In the course of construction of highway curbs and the like, two distinct operations are required irrespective of the means by which the paving materials are formed into structures. Thus, it is initially necessary to prepare the ground surface upon which the paving material is to be placed in order to remove loose material from the surface and to provide a predetermined depth sufficient to allow the required thickness of paving material. Furthermore, depending upon the methods by which the paving material is placed on the prepared surface, it is also often desirable to prepare a smooth and continuous surface so that the foundation of the paving material will be firm and compact and so that the paving material can obtain a smooth and continuous upper surface.
Following the preparation of the ground surface, the second operation is thereafter performed by placing the paving material on the ground surface and forming such into its desired shape. When extensive and continuous strips such as curbs, ditches, gutters, barrier walls, or the like, are to be formed, the use of a slip form paver has been found efficient and productive of consistent and uniform structures. In operation, paving material such as concrete is fed into a hopper on the paver which opens below into a slip form mold carried by the paver immediately above the ground surface. As the paver progresses, the concrete is extruded from the mold in a profile as determined by the shape of the mold and in a consistency that can be controlled by the forward velocity of the paver or the operation of compacting or extrusion means. In addition, improvements have been made to the paver, such as in U.S. patent to Smith U.S. Pat. No. 3,749,504, that permit automatic control of several functions of the paver. Thus, the direction of the paver and elevation of the mold can be automatically adjusted according to a control line or stringline which defines the predetermined direction and elevation.
During the early course of curb construction, the preparation of the ground surface and the forming of the structure were performed in two separate operations and with different apparatus. One apparatus previously used for surface preparation employs a trimmer having a rotatably mounted, transverse shaft with cutting members projecting radially therefrom. As illustrated in U.S. patents to Miller et al U.S. Pat. No. 4,041,623, and Brown, U.S. Pat. No. 3,693,722, the cutting members were often arranged helically about the shaft so that by the rapid rotation of the shaft substantially all of the ground surface was excavated when the trimmer was passed thereover. A blade or scraper followed the cutting members in order to level and smooth the remaining irregularities.
Because of the traditional design of the trimmer, its compatability with other paving apparatus and, particularly, slip form pavers was limited. Thus, the arrangement of cutting members introduced excessive vibration that was not conducive to the smooth operation required for uniform structures. Furthermore, the unwieldy structure and frequently complicated drive mechanisms of the trimmers restricted their adaptability for simultaneous operation with the pavers.
Attempts have been made to combine the ground preparation and structure formation functions so that both could be performed simultaneously and with the same machine. Thus, as in U.S. patent to Godbersen U.S. Pat. No. 3,779,661, a trimmer of conventional design was disposed laterally in advance of a floating mold, whereby the ground surface is graded at the elevation and position as determined by the position of the paver frame to which the trimmer was mounted. The trimmer is illustrated as having a width substantially greater than the width of the mold, and as will be apparent, the excessive width of the trimmer results in additional preliminary surface preparation and substantially increased operating power.
It has also been proposed to utilize a conventional trimmer of substantially the same lateral width as that of the mold in machines of this type. While this construction reduces power consumption, difficulties were encountered in that the trimmer, which was fixed forwardly of the mold, could not be made to conform to the intended path for the molded strip during curvilinear segments. In this regard, paving machines are conventionally guided by means of an external control line which is positioned in a predetermined relation with respect to the desired positioning of the strip of paving. Where the trimmer was mounted forwardly of the mold, the trimmer would not begin to follow a curvilinear path until the directional control for the mold began to follow the curvature in the control line. Thus, the radius of curvature as defined by the center of the path of the mold and predetermined by the curvature of the control line would not consistently equate with the radius of curvature as defined by the center of the trimmer's path, and the trimmer's path would not be maintained at a constant distance from the control line and in the desired path of the mold. Stated in other words, the trimmer did not have the ability to grade a section of the ground surface in the path of the mold which was toward the center of curvature, and extraneous ground surface area outside the path of the mold and remote from the center of curvature would be graded.
As a consequence of this limitation, the mold would possibly be forced to pass over areas of ground surface that had not been graded, thereby risking damage to the mold and providing an irregular and inconsistent foundation for the structure. Furthermore, the grading operation along inside curves would seemingly interfere with the control line or come prohibitively close to the control line for efficient performance. Also as a result of this deficiency, the rear wheel support on the side of the operation could abruptly change elevation when entering an improperly graded area and constant adjustment would thereby be required. Efficient operation would consequently be inhibited because of the need for continuous attention and correction of the operation.
It is accordingly an object of the present invention to provide a self-propelled apparatus that is adapted to concurrently grade a ground surface and slip form a continuous strip of paving material along the graded surface, such that the ground surface is graded substantially coextensively with the successive placement of the paving material.
It is another object of the present invention to provide a self-propelled apparatus that performs concurrent grading and slip forming operations along a curvilinear path while closely maintaining the lateral alignment of the graded ground surface with the placement of the paving material. In this connection, it is also an object of this invention to provide the means to perform the concurrent grading operation so that the radius of curvature of the graded path, may be made to consistently equate with the radius of curvature of the continuous strip of paving material.
It is a further object of the present invention to provide an apparatus of the described type that avoids grading excessive ground surface to thereby minimize the power requirement, and which also avoids the non-preparation of surface area upon which the paving material is placed.
Another object of this invention is the provision of an apparatus having a transverse trimmer which is adapted to operate without excessive or interfering vibrations whereby the successive grading and slip forming functions can be performed either independently or concurrently.
Still another object of the invention is the provision of a simplified reversible drive system for the trimmer which permits convenient operation in the presence of adjacent obstacles and obstructions, as well as the ready clearing of debris from the trimmer.